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Reduction of Technetium by Fe(II) associated with reduced clay mineral nontronite


EMSL Project ID
25610

Abstract

Because clay and clay-like minerals are commonly present at DOE sites (smectite, illite, chlorite, biotite), and they are potential backfill materials for nuclear waste repositories, the interaction of clay minerals with metal contaminants such as Tc is important. Smectite clays have a layered structure with a large interlayer space. As a result, smectites have sufficient ion-exchange capacity and hydrothermal stability to be viable as storage media for hazardous waste. Smectite contains Fe(III) in the structure, and once reduced, Fe(II) can exist as four different species: aqueous (virtually negligible), exchange (interlayer) site, edge (amphoteric/variable charged) site, and structural site. The objective of this research is to examine the relative reactivity of these Fe(II) species in biologically and chemically reduced nontronite, an Fe-rich smectite, toward technetium reduction. This determination is critical for our long-term goal of designing efficient means to reduce and immobilize Tc(VII) and other metals in field-scale applications. This objective fits well within the EMSL mission and the EMSL science theme.

Two well-characterized clay minerals, Fe-rich nontronite (NAu-2) and Fe-poor Na-montmorillonite (SWy-2) will be used in this research. Cation exchange capacity, surface area, and Fe(II) sorption isotherm and edge have been measured and these properties are similar between the two minerals. Two end members will be prepared with Fe(II) sorption, where 57Fe will be sorbed on the exchange sites and the edge sites under controlled pH and ionic strength conditions. The structural Fe(II) end member will be prepared by reducing a small extent of Fe(III) in NAu-2 by Na dithionite. Mössbauer parameters will be established with these end members. Tc(VII) reduction will be followed to determine the capacity and the rate of Tc(VII) reduction by each of these end members. Mixtures of these end members will then be created and used to reduce Tc(VII) to gain an understanding of the relative reactivity of each Fe(II) species towards Tc(VII) reduction. Finally, Tc(VII) reduction will be performed using chemically and biologically reduced NAu-2, and the reactive reactivity of Fe(II) species will be determined in the context of these above three end members.

Project Details

Project type
Large-Scale EMSL Research
Start Date
2007-05-25
End Date
2010-09-30
Status
Closed

Team

Principal Investigator

Hailiang Dong
Institution
Miami University

Team Members

Michael Bishop
Institution
Miami University

Ravi Kukkadapu
Institution
Environmental Molecular Sciences Laboratory

Related Publications

Bishop ME, H Dong, RK Kukkadapu, C Liu, and RE Edelmann. 2011. "Bioreduction of Fe-bearing clay minerals and their reactivity toward pertechnetate (Tc-99)." Geochimica et Cosmochimica Acta 75(18):5229-5246. doi:10.1016/j.gca.2011.06.034
Yang J, RK Kukkadapu, H Dong, ES Shelobolina, J Zhang, and J Kim. 2012. "Effects of Redox Cycling of Iron in Nontronite on Reduction of Technetium." Chemical Geology 291:206-216. doi:10.1016/j.chemgeo.2011.10.013
Zhang G, H Dong, H Jiang, RK Kukkadapu, J Kim, DD Eberl, and Z Xu. 2009. "Biomineralization Associated with Microbial Reduction of Fe3+ and Oxidation of Fe2+ in Solid Minerals ." American Mineralogist 94(7):1049-1058.